>> i've done that. >> yes, you have. that's going to d >>> tonight from japan, this is "world news," reporting on the disaster in the pacific. now, there are four. four troubled nuclear reactors at one site. what happens if they all melt? and who are the 50 brave workers who agreed to stay inside and try to save everyone else? >>> we go out with rescue crews, calling out for signs of life in the rubble. "make a noise," they say. "is anybody there?" hello? is anybody there? is anybody there? and survivors did emerge today. >>> and we tell you what is the real danger for the united states. what about that run on potassium iodide pills? >>> and, on "world news," lessons for all of us, from survivors of that hiroshima radiation 60 years ago. >>> good evening to everyone in the united states. here in japan, as we said, there are 50 workers inside a nuclear power plant, and they are battling the complete unknown at this moment. trying to prevent a nuclear power meltdown. and in this breaking news, we have received word that there is another fire, a new fire under way at one of those reac